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From what I understand, it is correction factor based. So, X.XX (One . Tenths Hundredths). Similar to that of a dyno.

So go fill up your gas tanks at the gas station. Reset the OBC's MPG readout on the instrument cluster and the odometer mileage. Drive around the way you usually do until you have consumed about 50-75% of your gas tank. Go back to the gas station and refill your gas tank. Then it is a two step process.

1) Read out what the OBC says the MPG is.
2) Manually calculate what your MPG from the odometer mileage divide by the amount of gas you put in your car.

You will find that the MPG you calculate will be lower than what the OBC says. I am assuming that the correction factor is percentage based.

Looking through the WDS the OBC doesn't have a discrete fuel consumption signal wire, it is computed by the cluster directly from data off the CAN bus.

If that is the case, the ONLY way to correct would be through software.

CAN is 1/2 the reason I converted my M54 to OBD1.

The correction factor is in the instrument cluster, not the OBC. So using what you said, I am trying to change how the instrument cluster calculates the data off the CAN bus to display to the driver. What am I missing here?

In any case, I'll try this when I get my car back. Although I do have INPA to try it with if this doesn't work.

From what I understand, it is correction factor based. So, X.XX (One . Tenths Hundredths). Similar to that of a dyno.

So go fill up your gas tanks at the gas station. Reset the OBC's MPG readout on the instrument cluster and the odometer mileage. Drive around the way you usually do until you have consumed about 50-75% of your gas tank. Go back to the gas station and refill your gas tank. Then it is a two step process.

1) Read out what the OBC says the MPG is.
2) Manually calculate what your MPG from the odometer mileage divide by the amount of gas you put in your car.

You will find that the MPG you calculate will be lower than what the OBC says. I am assuming that the correction factor is percentage based.

Having a correction factor of 1.17 would increase your gas mileage wouldn't it? That wouldn't make sense unless your car is more efficient now with the TS.

Quote:

Originally Posted by NickG@TechniqueTuning

The OBC is part of the instrument cluster on the E46

Well that confuses things a little bit. hoverguy says calculation is done in the instrument cluster and not the OBC. However, the OBC is inside the instrument cluster. So how does the data get to the driver? OBC->Instrument Cluster->Driver?

I haven't been able to change my MPG correction factor through the instrument cluster; has anyone else been able to? Test 20 does not indicate any data with the tests locked or unlocked. Neither am I able to access sub-menus to input data. Has anyone else tried it with success?

I think it's time to dig this thread up. What are you guys doing about OBC being way off?

I haven't found anything I can do. I would really like my OBC to function as designed; I'm willing to pay for the option, but can't find a way to do it. It's one of the unadvertised trade-offs you have to put up with when you go FI.